JPH0567184B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The invention relates to the field of electromagnetic radiation in printed circuit boards and similar circuit packages.
The present invention relates to a method and apparatus for locating high level sources of radiation.

PRIOR ART AND THE PROBLEM SOLVED BY THE INVENTION Telecommunications regulatory authorities in many countries require that electromagnetic emissions from computing devices and other digital devices be limited to prevent electromagnetic interference with licensed wireless communications. introduced regulations requiring For example, in the United States, the Federal Communications Commission has introduced Part 15, Subpart J of the FCC Rules, which provides testing methods and limitations.

Means for Solving the Problem One method of limiting radiation is by mounting the device within a shielded enclosure that acts as a Farady cage. this is,
This proves to be expensive due to the numerous treatments required to ensure that the shielding is not compromised by electromagnetic leakage through enclosure openings or external electrical connections. Thus, special conductive gaskets to the electrical bonding panels and radio frequency filters of all wiring exiting the device are required. A cheaper method in the long run is to
The goal is to ensure that electronic components do not actually generate high levels of electromagnetic radiation. Therefore, an important tool in circuit board design is a method for easily and accurately locating and measuring electromagnetic emissions from active circuit boards.

Using known systems, a prototype circuit board package is placed in an anechoic chamber-like environment free of any electromagnetic interference. A monitoring device is then assembled in spaced relation to the circuit board or device to ascertain significant electromagnetic emissions.

This does not actually help in determining exactly where electromagnetic radiation is high on the circuit board. In contrast, more localized monitoring devices are required.

According to an aspect of the present invention, in an electromagnetic radiator test device for testing an electromagnetic radiator, the electromagnetic radiator is arranged at a predetermined position having a known spatial arrangement in close proximity to the electromagnetic radiator, and probe means for providing an electrical output; probe selection means for sequentially addressing particular probe means; analysis means for analyzing the electrical output from the probe means to obtain a measurement of an electromagnetic radiation level; and map creation means for creating a map representing the electromagnetic radiation level at each predetermined position near the radiator from the measured values.

Preferably, in an electromagnetic radiator test device for testing electromagnetic radiators, the probe means comprises at least one wire loop and diode, which wire loop and diode are connected between corresponding row and column conductors from the probe selection means. connected in series.

Preferably, in an electromagnetic radiator testing device for testing electromagnetic radiators, the map creation means displays a map created corresponding to a known spatial arrangement of predetermined positions, each measurement value corresponding to an associated predetermined position. displayed on the map.

According to another aspect of the invention, an electromagnetic radiator test apparatus for testing an electromagnetic radiator further comprises means including a map of reference level data of electromagnetic radiation levels previously obtained from a reference radiator; and means for comparing radiation level measurements and said reference level data and providing a difference therebetween.

Examples Embodiments of the invention will be explained below by means of examples with reference to the accompanying drawings.

Referring in detail to the drawings, FIG. 1 shows a block diagram of an electromagnetic radiation scanning system. The system includes a probe array 10 driven by a decoder and driver circuit 12, a measurement receiver 14, a signal processor 16, and a controller 1.
8, and a visual display device 20. The probe array comprises a series of probe means in the form of probes 22 arranged at predetermined positions in a planar grid arrangement.

As shown in FIG. 2, the probe array is supported by a multilayer printed circuit board 50.
Each probe consists of two series-connected wire loops 24, 26, which are connected to one another on the surface of a printed circuit board on which an array (horizontal as shown) of the electromagnetic radiators to be tested is placed. Can be mounted orthogonally. A current is induced in each loop proportional to the electromagnetic flux in a direction perpendicular to the plane of the loop. The area of each loop is intermediate between the large area required for probe sensitivity and the small area that allows more probes to be packed into the array to increase the resolution of the scanning device. ). A suitable intermediate region is 0.04
square inch (approximately 0.256 cm ² ). Crossed probes are used to provide omnidirectional properties.

Although not described in this embodiment, yet another loop attached perpendicular to another loop is used to measure electromagnetic radiation perpendicular to the plane of the array. A single loop can be used for measurements in a single direction.

The circuit board package 39 to be tested is placed in close proximity to the scanning array so that changes in the magnetic field produced by the current in the broad conductor 41 cause a corresponding current in the probe 22. Induce. These induced currents are
Measured by 4. The array of probes is electronically scanned using decoder and driver circuits 12R, 12C, and each probe is further connected to a receiver.

Typically, electromagnetic radiation scanning is performed over a range of frequencies. Priority is given to those signals on the board with the fastest repetition rate. Only signal harmonic frequencies that fall within the scope of a particular application need to be considered (e.g., for FCC Part 15J requirements)
30MHz to 1000MHz). Alternatively, the total radio frequency divergent radiation of the circuit board is measured by conventional means using a radio receiver and antenna placed a distance apart, and the frequency of the radiation with the highest amplitude is determined by scanning the board. selected for.

Initially, receiver 14 is tuned to the particular frequency at which electromagnetic radiation is to be measured. The current induced in the addressed probe 22 generates a voltage across the receiver's terminating input impedance. The receiver has a variable bandwidth, for example 10KHz and 120KHz, and a selectable (peak or average) detection level to measure electromagnetic radiation at different frequencies.

The output of the receiver is sent to a signal processor 16 where it is digitized into a form suitable for input to a controller 18.

Controller 18 performs necessary housekeeping tasks such as addressing the columns of probes 22 in a predetermined order. It also sets receiver parameters such as frequency, bandwidth, and detection mode (amplitude or frequency modulation). Additionally, it directs the signal processor 16 in digitizing the signal from the receiver. Finally, controller 18 formats the data for input to visual display 20 according to whether the displayed map is required in contour or color format.

Selection of each probe 22 is accomplished by a diode matrix arrangement. for example,
In D16 (Fig. 1), switching or
A PIN diode 29 is connected in series with the loop in each probe. A particular probe at the horizontal row/column intersection places a positive voltage on one of the columns 32;
and is selected by applying a negative voltage to the appropriate horizontal row 30 to turn on the associated diode 29. The current induced in a selected probe, such as the probe designated by reference numeral 22 in FIG.
C20 and flows to collector bus 34 and receiver 14. From the selected probe 22 to the measurement receiver 1
The path leading to 4 is of controlled impedance, typically 50 ohms. 20MHz
At high frequencies above , the length of each horizontal row 30 becomes an appreciable portion of the wavelength.
To avoid variations in the received signal from signal reflections, the horizontal rows 30 are terminated by impedances, such as R9-R12, equal to the characteristic impedance of the transmission line, typically 50 ohms.

Signals are sent from probe 22 via stripline 36, which is connected to upper and lower ground planes 38 by bias 41 at repeating intervals, typically every 0.3 inches.
It has a side ground track 37 coupled to the lateral ground track 37. The anode end of the diode in each probe is C1~
It is AC grounded by a capacitor like C16. This is a surface-mounted capacitor that provides a high self-resonant frequency.

Control signals for probe selection are sent to lower layers 40, 42 of multilayer printed circuit board 50.
In use, printed circuit pack 39 is placed track side down (component side up) on top of the probe array, but separated from the probe by a thin insulating layer 44 to prevent electrical shorting. Ru. The printed circuit pack under test receives the expected signals and supply voltages in normal operation. The array is then scanned one probe at a time and the magnitude of the output from each probe is measured at receiver 14. The receiver output is then processed by signal processor 16 and sent to controller 18. A memory map is generated in the controller and computer aided design for a particular board.
(CAD) data is displayed. The data is formatted to show different levels of electromagnetic radiation as different colors or different contours. Eventually, the circuit elements responsible for the high radiation levels can be identified.

Although the invention has particular application in the circuit board design stage, it can also be used in production control to avoid producing boards that typically have high levels of electromagnetic radiation.

The scanning device of the present invention further provides
It is also used to measure EMI radiation.

This device can be used, for example, in fault diagnosis of printed circuit boards. Each printed circuit board (PCB), when energized and operated, has its own characteristic electromagnetic signature (or contour map) as measured by an electromagnetic scanning system. For a given type of PCB, a fault in a circuit conductor or component will cause this signature to change. This occurs because the signal current is interrupted (eg, by an open circuit), shunted (by a short circuit), or otherwise changed in amplitude or waveform by a defective component. By comparing the signature from the PCB under test with a reference signature obtained from a known good PCB, the location and nature of the fault can be determined.

When the fault is on a component of the circuitry that operates at direct current or very low frequencies where the EM scanning equipment is not sensitive, use a tracer signal of the appropriate frequency injected into the circuit in question. The scanning device is operative to map a path along this signal to aid in fault diagnosis.
An embodiment of this technique uses the tracer signal current as a power supply.
It is to inject between the ground terminals of the PCB to help trace the location of possible short circuits between these terminals.

This device also performs electromagnetic shielding evaluation (shielding
It can also be used in evaluation.
Good electromagnetic shielding requires that the shielding material (especially a thin conductive coating applied to the housing of a plastic device) be free of defects such as cracks and thin areas. Also, if the bond occurs between shielding panels, the electrical bond must be continuous. When such a shield is energized with radio frequency current from an external generator, areas of RF leakage at these defects are clearly displayed and located using a scanning device display.

Similarly, defects in a metal coating or sheet can be detected by a scanning device if the sample is properly energized with RF energy. This is done by injecting an RF current through the sample under test or by illuminating the sample with external RF radiation and then using a scanning device to observe the resulting pattern of RF current flow at the sample surface. It will be achieved. Defects such as cracks or poorly bonded metal panels appear as anomalies on the visual display.

In other applications, the scanning device operates in reverse. The scanning device port, which is typically coupled to a receiver, is instead coupled to a source of RF energy, such as a signal generator. When the scanning circuit operates, the applied signals cause an RF current to flow sequentially to each individual RF probe on the scanning device head. As a result, the scanning device operates in reverse and the detected RF
A magnetic field is generated at the probe location. The scanner head is placed in close contact with a PCB that is known to be sensitive to or exposed to RF, and the precise time of occurrence of PCB disturbance or malfunction is monitored. This relates to the particular probe of the scanning device that is being energized at the time. This technique is used to generate a map of PCB sensitivity to RF.

Depending on the particular application, appropriate adjustments are made to RF receiver sensitivity and bandwidth selection. The receiver is designed to respond to amplitude or frequency modulation. Alternatively, peak, average, RMS or log response signal detectors can be used.

As previously indicated, the display may display different radiation levels as different colors, color levels, contour maps, color intensity modulation maps, or simulated three-dimensional graphs. Known image processing techniques are used to increase the apparent resolution of the displayed image, or to enhance its contrast or information-to-noise ratio. The display intensity or color corresponding to each probe position may be expressed in binary to indicate a pass/fail situation, or it may be multiple times corresponding to successive measurements of some parameter of the circuit under test. quantization stages or levels.

Finally, in the scanning device itself, the probe size, aspect ratio, and number of loop turns can be selected according to the particular application. Optionally, the probe wire can have a magnetic core to increase probe sensitivity to low frequency electromagnetic fields, or an electric field shielding layer to eliminate undesirable electric field interference effects. The above scanning device has a flat rectangular probe array,
The scanning device is not limited to this format, and
Depending on the application, it can be arranged with probes arranged to form a cylindrical, spherical or disc-shaped support surface.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electromagnetic radiation monitoring device according to the present invention. FIG. 2 is a schematic perspective view, not to scale, showing one probe of a scanning array forming part of the apparatus. 12... Composite device/driver circuit, 14... Measurement receiver, 16... Signal processor, 18... Controller,
20...Display device, 30...Row conductor, 32...Column conductor.

Claims (1)

[Scope of Claims] 1. In an apparatus for testing an electromagnetic radiator: located at a predetermined position having a known spatial arrangement in close proximity to the electromagnetic radiator and providing an electrical output in response to electromagnetic radiation from the electromagnetic radiator; probe means; probe selection means for sequentially addressing particular probe means; analysis means for analyzing the electrical output from said probe means to obtain measurements of electromagnetic radiation levels; and measurements obtained by said analysis means. An electromagnetic radiator test device comprising: map creation means for creating a map representing the electromagnetic radiation level at each predetermined position near the radiator from the values. 2. The electromagnetic radiator testing device of claim 1, wherein the probe means comprises at least one wire loop and diode, which wire loop and diode are connected to corresponding row and column conductors from the probe selection means. An electromagnetic radiator test device characterized in that the electromagnetic radiator is connected in series between the two. 3. In the electromagnetic radiator testing device according to claim 1, the map creation means displays a map created corresponding to a known spatial arrangement of a predetermined position, and each measurement value is displayed at a related predetermined position. An electromagnetic radiator test device characterized in that the device is displayed at a corresponding position on a map. 4. The electromagnetic radiator test device according to claim 1, comprising: a map of reference level data of electromagnetic radiation levels previously obtained from a reference radiator; and a map of electromagnetic radiation level measurement values and the reference level. and means for comparing the data and providing the difference thereof.